The present invention relates to an apparatus for the measurement of sheet members over a wide range of thickness values and more particularly, to an apparatus employing air bearing calipers and a method for using the apparatus.
Air bearing caliper gauges, used to measure the thickness of a sheet material, are well known in the art. See for example, U.S. Pat. Nos. 3,528,002 and 4,107,606. The teaching of the prior art, however, is that the transmitter and receiver are each placed in a housing located on opposite sides of the sheet. Each of the housings is maintained at a constant distance from the sheet through the action of the air bearing. The disadvantage of lifting each housing unit, with the weight of each housing unit associated therewith, precludes the use of the air bearing caliper gauge of the prior art on sheet members that have a wide range of thicknesses. Moreover, the problems of accuracy and stability caused by an apparatus to measure the thickness of the sheet over a wide range is not recognized and the solution is not taught by the prior art.